The invention relates to an electric lamp having a light source arranged within,
A lamp vessel which is sealed in a vacuum-tight manner and made of glass having an SiO.sub.2 content of at least 95% by weight and having a pinched seal at an end thereof.
A metal foil having a first and a second end is included as a current lead-through conductor in the said pinched seal.
The metal foil being connected near its first end to at least one external current conductor, which is passed to the exterior from the said pinched seal.
The metal foil having a first and a second major surface and having near its second end on a first major surface a welding connection with an internal current conductor extending to the light source.
A metal auxiliary foil is near the second end of the said metal foil, which forms an additional connection between the metal foil and said internal current conduction.
Such an electric lamp is known as an incandescent lamp from JP UM Application No. 51-137898.
In the known lamp, the internal current conductor is enclosed, as far as it overlaps the metal foil, between said metal foil and the metal auxiliary foil. This construction has a number of great disadvantages. The end of the internal current conductor welded to the metal foil should be bevelled in order that the metal auxiliary foil can follow exactly the surface of the internal current conductor. Without this measure, there is a risk that, when the pinched seal is formed, the metal auxiliary foil is subjected to tensile stress and breaks. Another disadvantage is that cavities are formed between the two foils on either side of the internal current conductor. Consequently, the foils are subjected to a considerable extent to the atmosphere prevailing in the lamp. A further disadvantage is that the assembly of the current conductor to the light source can be manufactured only with great difficulty.
Certain electric lamps are very heavily loaded during operation. A high current of, for example, several tens of amperes flows through these lamps, which leads to high current densities in the pinched seal especially at the transition from the metal foil to the internal current conductor. This results in a strong development of heat in the pinched seal. The maximum permissible temperature of the pinched seal can thus be readily exceeded.
Exceeding of this temperature causes the metal foil and the external current conductor to oxidize so rapidly that the pinched seal bursts and the lamp becomes leaky before the calculated life of the lamp is attained. Therefore, it is of major importance that a lamp is available having a construction which keeps the temperature of the pinched seal sufficiently low during operation, so that the oxidation in the pinched seal does not determine the lifetime of the lamp.
A contribution to a temperature reduction is obtained by a suitable construction of the transition from the metal foil to the external current conductor. It is known, for example, to weld several external current conductors to the first end of the metal foil and to interconnect these current conductors outside the lamp. The temperature reduction thus obtained is insufficient, however, with heavily loaded lamps. A similar construction of the transition from the metal foil to the internal current conductors generally cannot be realized in practice.